The present invention relates to an optical disc drive.
Recently, an optical disc drive whose data recording density on an optical disc reaches up to 10 Giga bits/inch2 has been developed.
In such an optical disc drive, an objective lens is generally mounted on a carriage, and the carriage is made movable in a direction traversing the tracks of the data recording surface of the optical disc (i.e., the radial direction of the optical disc).
A magnetic head is also mounted on the carriage for applying magnetic field to the optical disc when data is to be recorded. In general, the magnetic head is mounted on the carriage via a relatively long elastic beam. When the disc revolves, an air flow occurs, and the magnetic head is lifted by the air flow so that the magnetic head is slightly apart from the data recording surface of the optical disc by a predetermined amount.
Such a magnetic head is located at an operation position, which is closely adjacent to the optical disc, when it applies the magnetic field thereto, while the magnetic head should be retracted (located apart from the disc by a certain amount) when the optical disc is to be inserted in or ejected from the optical disc drive so as to avoid the magnetic head from being damaged. Therefore, a mechanism for locating the magnetic head to the operation/retracted position is required in the optical disc drive.
Further, in the optical disc drive, a fine tracking is executed for locating a beam spot formed by the objective lens precisely on a track of the optical disc. For this purpose, the magnetic head as well as the objective lens may be moved in a direction traversing the tracks of the optical disc, and a mechanism therefore is required.
Recently, the mechanism for the fine tracking as well as the mechanism for retracting the magnetic head tend to be complicated, and simple mechanisms have been desired.
For the above object, according to the present invention, there is provided an optical disc drive, which is provided with: a light source unit that emits a collimated light beam; a carriage mounting an objective lens for converging the collimated light beam on a recording surface of an optical disc, the carriage being movable in a direction traversing data tracks of the optical disc; a lens actuator mounted on the carriage, the lens actuator having a movable unit, the movable unit being capable of moving the objective lens in first and second directions, independently, the first direction being a direction of an optical axis of the objective lens, the second direction being a direction on a plane parallel to the data recording surface of the optical disc; and a magnetic head mounted on the movable unit of the lens actuator, the magnetic head being capable of applying a magnetic field onto the data recording surface of the optical disc when data is to be recorded on the optical disc, wherein positional relationship between the objective lens and the magnetic head being substantially constant regardless of moving amount of the movable unit in the first and second directions.
Constructed as above, only by moving the movable unit of the lens actuator in the first direction, the objective lens as well as the magnetic head can be moved. Thus, the structure for moving the objective lens and the magnetic head can be made relatively simple, and compact in size.
Optionally, the magnetic head could be mounted on the movable unit via an elastic member.
In particular case, the magnetic head may be biased toward the data recording surface of the optical disc by the elastic member. In this case, the magnetic head is located slightly apart from the data recording surface of the optical disc due to an air flow caused by revolution of the optical disc.
Since the magnetic head is biased, the positional relationship between the magnetic head and the recording surface of the optical disc may be maintained even if the position of the data recording surface is varied while revolving.
Preferably, rough tracking is performed by moving the carriage in the direction traversing the data tracks of the optical disc, and fine tracking is performed by moving the movable unit in the plane parallel to the data recording surface of the optical disc.
Optionally, the movable unit is movable to locate the objective lens between an operation position, in the first direction, when data is recorded or reproduced, and a retracted position, in the first direction, when the data is not recorded or reproduced. The operation position is defined as a position at which the beam emitted by the light source is converged on the data recording surface, and the retracted position is defined as a position at which the objective lens is retracted from the operation position.
In this case, the magnetic head is also located at an operation position which is closely adjacent to the data recording surface of the optical disc when the objective lens is located at the operation position, and at a retracted position which is away from the data recording surface of the optical disc when the objective lens is located at the retracted position.
Further optionally, focusing may be executed by moving the movable unit in the first direction.
Still Optionally, the lens actuator may further include an actuator base mounted on the carriage, the movable unit may include a lens holder for holding the objective lens, and the lens actuator may further include a shaft standing on the actuator base, the shaft extending in a direction parallel to the optical axis of the objective lens, the lens holder being rotatably and slidably supported by the shaft.
In particular, the lens actuator may be provided with: a first electromagnetic system for moving the lens holder in the first direction; and a second electromagnetic system for rotating the lens holder about the shaft.
Further optionally, the optical axis of the objective lens may be parallel to and displaced from the central axis of the shaft by a predetermined amount.
Furthermore,the carriage may be movable in a radial direction of the optical disc.
Still optionally, the magnetic head may be mounted on the lens holder.